RB211(-535) separation

[Brenoch]

I was once taught that on a B757 RB211 installation (possibly on all RB211s) that if you suffer a dual fire detection loop failure you will get a fire warning. If the engine would separate from the airframe, I suppose that would cause a dual fire loop failure by nature.

Now, I've been through said separation-scenario in the simulator numerous times now but have yet to get the alleged fire warning.

Have I missed something fundamental or are the sims just not up to par when it comes to system simulation?

[3bars]

Will you not also lose the EEC during separation which tells the computers that the engine is running?!

[SMOC]

True, the loops and the "box" they communicate with are on the engine, they would have departed with the engine & possibly intact.

[flyboyike]

If I'm fairly certain the engine has separated, what do I give a flying bleep what other warning relating to the dearly departed engine I am or am not getting?

[aidey_f]

As always with sim malfunctions, it depends.
In this case, it will depend where you swing the software axe to remove the engine, what type of sensing loops they are, do you short the loops against the structure.
Ultimately, fly what's in front of you, the info in the instructor station won't give schematic refs for which widget broke and how.

[Old Fella]

Just wondered how many instances of "Engine Separation" have happened with B757's. I am pretty sure that regardless of what warnings might occur, the separation of an engine would be pretty obvious to the pax if not to the crew in the sharp end. Don't think it would be long before it was obvious that it has gone and any fire warning relating to that engine would be erroneous.

[N1 Vibes]

Fire detection should still work without engine running indications - otherwise if you had a fire on ground, shut down the engine, you would lose your indication.

[Old Fella]

N1 Vibes. The question relates to an Engine Fire Indication AFTER engine separation. If the engine has departed company with the aircraft the Engine Fire Detection medium has gone with it. The scenario described by Brenoch sounds to me much like an over enthusiastic Sim Instructor dreaming up unlikely scenarios.

[Hydroman400]

It will depend on the airframe but the fire wire or element 'signals's are usually routed back to the FPCU (Fire Protection Control Unit) which is a central unit that detects multiple fire, smoke events on the a/c. If both loops are damaged or the wiring, it is likely that the FPCU will see this as a o/c and detect it as an internal failure not an actual fire event. However, I know of some recent designs that have modified the logic in the FPCU to accomodate rare events like torching flame where in theory the jet could cut booth loops which may supress a fire warning when you don't want it to.

Not sure about the RB211 design but if a fire wire (thermistor) it will depend on the resistance and capcitance in the circuit and how the control units "sees" these parameters.

Just my tuppence worth.